Date of Award

Spring 2004

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)

Department

Federated Physics Department

First Advisor

Trevor Tyson

Second Advisor

Mark C. Croft

Third Advisor

Daniel Ely Murnick

Fourth Advisor

John Francis Federici

Fifth Advisor

Anthony Fiory

Abstract

The recovery of superconductivity in underdoped YBa2Cu3O6+y (YBCO) by exposure to bromine, iodine, chlorine and fluorine is a long-standing problem which has not been clearly resolved. The key question concerns the role of these halogens in the lattice. In order to shed light to this problem, we have performed multiple-edge x-ray absorption fine structure (XAFS) measurements about the Y K, Ba L3, I L3, Cu K and Br K-edges at room temperature on brominated (non-brominated) and iodinated (non-iodinated) YBCO single crystals. Our XAFS results at the Br K (brominated) and I L3 -edges (iodinated) reveal that bromine and iodine do not enter the perfect YBCO lattice.

However, the XAFS fitting results at the Br K and I L3-edges reveal that Br and I do occupy the Cu(l) sites of the oxygen deficient YBCO in nanoclusters. From the polarized x-ray absorption near edge measurements (XANES) at the Cu K-edge, the nanoclusters were found to be randomly oriented with respect to the "host" crystal and with respect to the polarization vector.

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